A method for synthesizing a ceramic thin film using a solution reaction (referred to as a "sol-gel processing") has attracted special interest recently. The sol-gel processing is a method comprising synthesizing an inorganic polymer precursor from an organic metal compound or a metal complex in a solution by using a hydrolysis reaction or condensation reaction; applying the solution on a substrate by means of a spray method, dipping method or spin-coating method to form a thin film; and subjecting the thin film to a heat treatment to form a functional ceramic thin film. The functional ceramic thin film is used as dielectric film, insulator film, protective film, etc. in electronic devices such as thin film capacitor, LSI, electroluminescent device and the like, and a formation technique by means of the sol-gel processing have been studied intensively. On the other hand, in addition to the above electronic devices, the sol-gel processing is applied for a surface treatment of functional glass or plastic, for example, anti-diffusion film of alkali, interference colored film, anti-reflection film, reflection film and the like.
The method for forming a thin film by means of the sol-gel processing has excellent characteristics such as temperature reduction of process temperature, freedom of composition, formation of uniform thin film on a substrate having a large surface area and the like.
However, there is no method of patterning a thin film, and a method of removing a thin film by conducting etching after formation of the thin film is popular. A complicated lithography step using a photoresist is required in order to conduct etching, and simplification of the step has been required.
Further, it has been studied to use a glass as the substrate for magneto-optic disc in view of durability, however, it's practical application is falling behind because of the largest disadvantage of the glass, i.e. a pre-groove can not be formed at low cost. For example, as the practical application of the sol-gel processing, there have been proposed a method of transferring a groove by a stamper while the gel is soft (Tohge et al., J. Am. Cream. Soc. 70, C13 (1987)) and RIE (Reactive Ion Etching) method wherein a photolithography method is combined with a dry-etching method after a SiO.sub.2 film was formed (Ota et al., Electronic Material, 27, 7, 57 (1988)). However, they are merely used for long-term storage in view of cost.
On the other hand, the present inventors have already proposed a process for dyeing a pattern using a silanol group produced by exposing an organic polysilane to ultraviolet light (Japanese Laid-Open Patent Publication No. 05-188215) and a method for coloring a pattern by dipping in a colored sol solution comprising a metal alkoxide containing a dye or a pigment as a raw material (Japanese Patent Application No. 4-68243). Further, the present inventors have studied to develop a function other than a colored pattern using a sol.
As described above, the present inventors have studied intensively. As a result, the present invention has been accomplished.